In the field of clinical chemistry, diagnostic analyses often consist of chemical reactions in which an analyte is reacted to form an observable product at a rate proportional to the amount of analyte still present in the reaction. This is referred to as a first order reaction, wherein the rate of product formation is proportional to the first order of the reactant, i.e., the analyte. First order kinetic reactions produce an exponential concentration vs. time profile that is modeled mathematically by an exponential equation wherein an observable response proportional to the concentration of the reaction product is related to reaction time and a reaction rate constant. The observable response may be, for example, a colorimetric determination of the concentration of a reactant or a reaction product. The rate constant of the reaction is typically variable with temperature and usually increases with increasing temperature.
Situations are frequently encountered where reaction profiles are not strictly first order, but are close enough to be approximated by a first order kinetics exponential through much of the reaction's time course. This is often the case with enzymatically catalyzed reactions where the reaction rate (at a given temperature) is a function of both enzyme and analyte (reactant) concentration. Characterization of the reaction end point usually requires that the reaction be carried to completion. The reaction may in some instances be speeded up by increasing either temperature or enzyme or other catalyst concentration. However, in many cases a reaction must be carried out at ambient temperature, and even with increasing the enzyme or catalyst concentration, the time needed to reach a limiting observable response may require long endpoint times.
Many medical diagnostic tests for reactions of first order or pseudo-first order kinetics are based on end point assays that are carried out under ambient temperature conditions. Most such assays require that the amount of time allowed for reaction be sufficient to obtain a reproducible value for an observable response associated with the end point of the reaction. Assays for the detection of chemical and biochemical compounds may thus take minutes or hours to obtain a reasonably accurate observed response or value that is indicative of the reaction end point.
The wait time required to obtain a reaction end-point for many clinical and biochemical assays can reduce the productivity of medical laboratories and may have unacceptably long endpoint times in emergency situations. Further, many commonly used assays, such as blood glucose level tests for diabetics and thromboplastin-based tests for anticoagulation patients, are increasingly performed by lay persons in non-clinical settings. Lack of skill or patience in making measurements over the necessary time period by such lay persons can require inconvenient repetition of test measurements, increase the risk of obtaining erroneous diagnostic data, and can ultimately lead to non-optimal clinical outcomes associated with test measurements that are improperly carried out.
There is accordingly a need for methods that reduce the overall assay time for medical diagnostic tests, and which facilitate and simplify such tests. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.